Escape pipe symbol in Spring REST Docs

I need to document an API that accepts a JSON represented by this class:

public class Message {
@NotNull(message = "Sender cannot be null")
private String sender;
@Pattern(regexp="HI|HELLO",message = "Message can be only 'HI' or 'HELLO'")
private String content;
// Constructor, Getters and Setters..
}

Spring Docs autogenerates the following snippet:

.Request fields:
|===
|Path|Type|Constraints|Description

|sender
|String
|Must not be null
|Sender of the message

|content
|String
|Must match the regular expression `HI|HELLO`
|Content of the message

|===

Which is used by Asciidoctor to create a table in the pdf. However, in the pdf, the table is broken (because of the pipe):

How can I escape the pipe within the regular expression?

I found this issue, but seems to be related to another project.

This is the test class to generate the documentation (JUnit5):

@WebMvcTest(HomeController.class)
@AutoConfigureRestDocs(outputDir = "target/snippets")
public class HomeControllerTest {
@Autowired
private MockMvc mockMvc;
@Test
public void postMessageTest() throws Exception {
ConstrainedFields constrainedFields = new ConstrainedFields(Message.class);
this.mockMvc
.perform(post("/message").content("{\"sender\":\"Marc\",\"content\":\"HI\"}")
.characterEncoding("utf-8")
.contentType(MediaType.APPLICATION_JSON))
.andDo(print()).andExpect(status().isOk())
.andDo(document("home-message", requestFields(
attributes(key("title").value("Request fields:")),
constrainedFields.withPath("sender").description("Sender of the message"),
constrainedFields.withPath("content").description("Content of the message")
)));
}
private static class ConstrainedFields {
private final ConstraintDescriptions constraintDescriptions;
ConstrainedFields(Class<?> input) {
this.constraintDescriptions = new ConstraintDescriptions(input);
}
private FieldDescriptor withPath(String property) {
return fieldWithPath(property).attributes(key("constraints").value(
// Let's assume there is only one constraint for each property
constraintDescriptions.descriptionsForProperty(property).get(0)));
}
}
}

The full project to reproduce the issue is here.

probably not the best solution, but, after doing little research, I found out that a simple \ character is enough to escape pipe character in asciidoctor documents (source). our goal then is to get this line in the .adoc snippet:

|Must match the regular expression `HI\|HELLO`

this is the method that extracts "constraints descriptions" in your code:

private FieldDescriptor withPath(String property) {
return fieldWithPath(property).attributes(key("constraints").value(
// Let's assume there is only one constraint for each property
constraintDescriptions.descriptionsForProperty(property).get(0)));
}

here we have "full control" over the text that will be written in the .adoc. we could for example take the constraint description from constraintDescriptions.descriptionsForProperty(property), apply our escaping and than pass the escaped string to .value():

private FieldDescriptor withPath(String property) {
// Let's assume there is only one constraint for each property
String desc = constraintDescriptions.descriptionsForProperty(property).get(0);
desc = desc.replace("|", "\\|");
return fieldWithPath(property).attributes(key("constraints").value(desc));
}

this will produce the escaped line in the .adoc and will be correctly rendered in the .pdf: